DISSERTATION RESEARCH: Vegetation structure constraints on ANPP in arid ecosystems: Assessing the meristem limitation hypothesis

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Although annual precipitation is considered the major control of plant production in arid and semiarid ecosystems it accounts for only 20-40% of the interannual variability of plant production. This doctoral dissertation project is based on the hypothesis that precipitation is indeed an important control but that there are lags in the ecosystem response to changes in precipitation that mask the precipitation-productivity relationship. The student will explore the role of meristem (plant tissue capable of dividing and giving rise to new organs) limitation in creating those lags with a manipulative experiment of incoming precipitation using a combination of passive rainout shelters and irrigation in the Chihuahuan Desert in New Mexico. The experimental design creates sequences of dry and wet years and will elucidate whether there is meristem limitation, whether the magnitude of the limitation is proportional to the rainfall deviation and finally whether the effects of preceding dry years are similar but of opposite sign of the effect of wet years. Results from this project will contribute to the understanding of the effect of climate variability on carbon sequestration, primary production, cattle production and the process of shrub encroachment, issues important to everyone from cattle ranchers to city governments concerned about water supplies. Such stakeholders are interested in understanding the consequences of expected climate change (increased temperature, decreased precipitation, and increased interannual variability) on the ability of their land to provide ecosystem services on which their well-being depends.